This application claims the priority of German patent document 199 21 675.4, filed May 11, 1,999 and PCT International Application No. PCT/EP00/04273, filed May 11, 2000, the disclosures of which is expressly incorporated by reference herein.
The invention refers to an electronic monitoring unit for an electrical energy storage system which includes multiple series connected components and particularly to a multiple cell or multiple block battery, where the monitoring unit contains a corresponding number of measuring devices, with one device allocated to each storage component, and where each device measures at least one storage status parameter for the associated storage component. For simplicity, the term xe2x80x9celectrical energy storage systemxe2x80x9d is in this instance defined to include also energy producers, such as fuel cell systems, which generate electrical energy from non-electrical stored energy, such as mechanical or chemical energy, in addition to simple storage devices, such as batteries.
Such monitoring units monitor the status of individual blocks or cells of the electrical energy storage system, such as a traction battery of an automobile with an electrical or hybrid motor, or a stack of fuel cells, such as in a fuel cell vehicle. The storage status indicator typically monitored are specifically the electrical voltage deriving from the storage component being monitored as well as the temperature and pressure of the storage device. The monitoring serves, among other purposes, to determine the present storage status of the storage devices due to variable self-discharge and aging of the series connected storage devices, so that corrective measures may be taken if needed, such as charge transfer between storage devices to keep the charge levels essentially equalized and to avoid having the xe2x80x9cweakestxe2x80x9d storage device determine the total capacity of the electrical energy storage system.
German Patent Document DE 195 03 917 C2 discloses a monitoring unit of the type described above, in which the individual measuring devices are connected to a serial data bus, formed as a ring, which is also connected to a central data processing unit. The measurements are transferred from measuring device to measuring device around the ring, and each measuring device retrieves the information it requires from the data packet and adds its own measuring data, such as voltage and temperature of the respective storage device. The central data processing unit can then evaluate the measurement data to determine the status of the individual storage components and thus the status of the complete energy storage system.
In an additional type of battery monitoring system, the measuring devices allocated to each individual storage component are connected in parallel to a joint signal connection. Such a unit, as disclosed in European Patent Document EP 0 277 321 A1, transfers the measurements to a central data processing unit from each measurement device in turn as polled.
One object of the present invention is to provide an electronic monitoring device of the type described above, which requires comparatively little cabling and control, and which provides reliable data regarding the status of the energy storage device by processing of one or more relevant measurement parameters.
This and other objects and advantages are achieved by the present invention which provides an electronic monitoring device that requires relatively little cabling and allows the determination of at least the generally most interesting and most relevant extreme values of the parameter or parameters in use, to indicate the status of the electrical energy storage system.
For this purpose, in the system according to the invention measurement parameters are transferred successively from one measuring device to the next, with each successive measuring device evaluating the measurement value for its associated storage device with respect to the measurement data as received, according to one or more prespecified evaluation criteria. In the case of an extreme (that is, maximum and minimum) value criterion, for example, this evaluation consists of determining whether the current measurement is larger or smaller than the previous extreme value as received, and then transferring the thus possibly modified extreme value to the next measurement device. The measurement devices do not need to be normed to their dielectric strength.
In one embodiment of the invention, the measurement devices are connected in parallel to a joint signal connection. These devices coordinate the transmission of the measurement parameters in parallel into the signal wiring, so that the wiring contains the identifiable extreme values on an overall basis ready for evaluation. Such configuration requires no separate signal wiring between each pair of measurement devices, and no separate evaluation process in the measurement devices themselves. Rather, evaluation occurs automatically through overlays of the measurement data from the various measurement devices in the common signal wiring. The measurement devices may be triggered simultaneously without run time error. In a variation of this embodiment the measurement devices are connected to the joint signal wiring via a capacitance or an inductance and are thus galvanically decoupled.
In a further embodiment of the invention, the measurement devices may be switched on and off by operation mode control signals from the control unit, with the devices using a minimum of electricity while turned off. Depending on the system specifications, the signals from the control unit may be sent in parallel to the measurement devices over a joint signal wire, or may be passed sequentially from one measurement device to the next. By use of these operation mode control signals, any measurement devices not presently required may be held in a deactivated state to save on electricity.
In a further embodiment of the invention, the measurement devices may be switched among various measurement modes by measurement mode signals from the control unit, such as between evaluation of the maximum or minimum of a particular parameter or among evaluations of various parameters. Thus, various measurements may be available at various times on the same signal wire.
In still another embodiment of the invention, the measurement devices may be subdivided into active and passive measurement devices. Active measurement devices are defined as those with a full range of functions, while passive measurement devices are those which are in a state where they can transmit signals received (such as measurements from an adjacent measurement device), but do not modify such transmitted signals on the basis of their own measurements. Thus, the system with sequential transmission and evaluation of the measurements may select measurement devices as desired to participate actively in the measurement of evaluated parameters.
In a further embodiment of the invention, the measurement devices transmit the measurement signal in a pulse-width modulated format, with the pulse width representing the respective measurement value. This enables very simple extreme value determinations within the framework of a corresponding extreme value evaluation criterion, and avoids error accumulation in the process of serial transmission of the measurement data from measurement device to measurement device. An alternative variation of this embodiment includes conditioning of the measurement signal such that each signal consist of a pulse, which is sent with a delay peculiar to the respective measurement value. This type of measurement signal will likewise allow for very simple extreme value determinations. As a further alternative, conditions the measurement signal may be conditioned as a constant current signal, which likewise allows for a simplified determination of the extreme value.
Finally, in a further configuration of the invention, the monitoring system enables a dissipative equalization of the charge status, each of the measurement devices containing an electrical resistance for discharging those storage components in which an excessively high charge is detected sufficiently to keep the maximum difference of the charges among the storage components below a prespecified tolerance value.